Process of making essentially pure silica fiber bats



June 4, 1963 D. LABlNO 3,

PROCESS OF MAKING ESSENTIALLY PURE SILICA FIBER BATS Original Filed May6, 1953 2 Sheets-Sheet 1 uvvszvrox. v 06 mm OQMM BY 20556 53 800 01ATTORNEYS June 4, 1963 D. LABlNO 3,092,531

PROCESS OF MAKING ESENTIALLY PURE SILICA FIBER BATS Original Filed May6, 1953 2 Sheets-Sheet 2 (QM BY ATT NEYS IN V EN TOR.

c95kgfd United States Patent 3,092,531 PRQQESS 01F MAKENG ESfiENTlALLYPURE SELICA FIBER BATS Dominick Labino, Manatee, Ghio, asslgnor, bymesne assignments, to .lohns-Manviile Fiber Glass ind, Cleveland, Unit),a corporation of Delaware Continuation of application fier. No. 353,348,May 6, 1953. This application Feb. 1, 1956, Ser. No. 562,722v 2 Claims.(Cl. 15624) This invention relates to the production of fibers of silicafor use in industrial applications which require a material of superiortensile strength and high insulation qualifies.

This application is a continuation of my copending application SerialNo. 353,348, filed May 6, 1953, now abandoned, which in turn is acontinuation-in-part of my now abandoned application Serial No. 304,150,filed August 13, 1952.

In my co-pending application there is described a fiber which consistsessentially of and which exhibits the properties of substantially puresilica. As described in that application the silica fiber is produced byfirst forming a fiber of soluble sodium silicate and then leachingsodium oxide from the sodium silicate to attain the silica in fiberform.

It is within the contemplation of this invention .to pro vide a productwhich consists essentially of silica fibers and which has superiorstrength properties. This objective is attained, generally speaking, byforming a compact bat of blown fibers of an alkali silicate and thenleaching the alkali therefrom while maintaining the fibers in bat form.Quite surprisingly the compacting of the fibers and the subsequentleaching in the compact form does not cause a physical deterioration ofthe fibers, but the bat, on the contrary, exhibits essentially goodstrength properties, rendering it suitable for many uses where morefragile bats of fibers would be destroyed.

Preferably in the process of invention the fibers of alkali silica arewound into a tight compact bat as they are produced, the individualfibers interlacing to form a unitary mass. Then preferably a series ofthese masses is arranged in tiers and while so arranged the alkali isleached from the compacted fibers. During th leaching the masses arepreferably maintained under a slight pressure, sufiicient to preventswelling of the fibers upon passage of the leaching agent therethrough.This insures that the resultant bat will have an optimum strengthcondition.

The leaching agent may be water or an acid which does not attack thesilica fiber produced by the leaching; that is phosphoric acid is notconsidered suitable although organic acids as well as inorganic acidsmay be employed.

The leaching operation may be performed with water at room temperatureover a period of about hours, or it may be performed with water at theboiling point in a lesser time. Where acid is employed a time of about 1hour for the extraction of the oxide may be achieved if the acid is at ahigh temperature, for instance 212 F. More specifically, the conditionsare substantially those set out in my co-pending application referred tohereinbefore.

This leaching operation not only removes the alkali and oxide but italso occasions the pickup of water molecules by the silica and theimmediate product of the leaching operation is a hydrated silica or asilica containing chemically combined water. These chemically combinedwater molecules are not removed when the mass of fibers is subjected todrying conditions at about 212 F. but are driven off when thetemperature of the plied mass is raised above 1000 F., and to attainpure 3,fifi2,53l Patented June 4, 1963 silica product it is necessary toemploy in theprocess of invention a temperature of about 1000 F.

While I prefer to employ fibers of the alkali silicate which havediameters of about 1 micron or less, I have found fibers having adiameter up to about 2% microns respond exceedingly well to the processand may be employed to produce the substantially pure silica fibers inbat form which constitute the product of this invention.

It is also to be noted in this connection that while it becomes moredifficult to remove the alkali compound as the fiber size increases, inmany applications the presence of a small amount of alkali is notobjectionable, although such fibers it is to be stressed do not exhibitthe optimum properties obtainable with the fibers which consistessentially of silica.

Glasses found to be most suitable for attaining the strong silica batsare alkali glasses having a weight ratio of alkali oxide to silica inthe approximate ratio of about 1:4; such glasses soften at relativelylow temperatures and accordingly may be readily fused and drawn intolong thin strands which upon being subjected to a hot gas blast areblown into fibers having a diameter, depending upon specific conditions,of 2% microns or less; prefrably the conditions are such that the glassfibers formed are 1 micron or less in diameter, as this facilitates thesubsequent alkali-oxide extraction.

The fibers which are blown from the alkali glass are" collected on amoving belt and they appear as a white fiuffy fibrous mat. In theprocess of this invention the thus collected fibers are plied togetherto form a thick bat, and the plying operation is preferably performed bypassing the blown fiber as it is formed about a moving roll until thedesired thickness of bat is attained. This operation causes the fibersand adjacent layers to interlace and to become compressed together; uponattaining of the required thickness the bat is cut from the roll andleached free from the alkali and generally, for economic reasons, it ispreferable that the series of bats, to which a slight pressure isapplied, are extracted at one time.

It is to be noted in this latter connection that it has heretofore, thatis prior to my co-pending application, been considered to besubstantially impossible to leach glass fibers free of alkali withoutcausing a destructive deterioration of the fibers; in fact, in thinstructural form alkali glasses containing only the alkali and silicahave been considered unsuitable for most purposes due to the destructiveaction of the alkali on the silica, particularly in the presence ofmoisture, the destructive action occur-' ring to such an extent that thethin structure disintegrates. Further it has been considered that fibersin this form would fragment readily and could not be suitably employedfor the production of useful articles. However I have found that if thealkali oxide is removed from the glass in accordance with the teachingsof my co-pending application that such deteriorating action does notoccur and that the fibers of the alkali silicate during the leachingprocess require no external support or protection whatever; further Ihave found quite unexpectedly that it is possible to leach bats having aconsiderable thickness completely free of the alkali while attaining abat of relatively high strength as a result of the process and that thismay be accomplished without binding the fibers of the bat individuallyor as a mass.

After the leaching of the 'bat the fibers thereof will, as notedhereinbefore, contain the water molecules which are apparentlychemically combined with the silica. The bat in this condition will havea slightly soapy feeling when dried at about 212 F. However whensubjected to a temperature in excess of about 1000 F. the chemicallycombined water is expelled and the resultant prodnot is a white spongymass in which the individual fibers are substantially indistinguishable;the interior of this product when exposed, as by tearing, very muchresembles a mass of cotton batting, as the fibers are substantiallyopaque and do not at ail resemble the filaments fr m which the fibersare derived. More specifically the product does not have an open fiberappearance, but is a soft coherent mass in which the individual fibersare substantially indistinguishable. These characteristics are attainedbecause of the close cohesion of the fibers and their contact with eachother during the production process.

The invention will be more fully understood by reference to thefollowing detailed description, including a specific example, and theaccompanying drawings Wherein:

FIGURE 1 is a schematic representation of apparatus used in theformation of the compact layered bats;

' FIGURE 2 illustrates a hat of fibers in a portion of the apparatus ofFIGURE 1;

FIGURE 3 illustrates equipment for effecting a leaching operation;

FIGURE 4 schematically illustrates an oven for the heating of theproduct in a production manner; and

FIGURE 5 is a view in section illustrating the product of invention.

Referring briefly to FIGURE 1 there is shown generally therein apparatususeful in the attainment of the attenuated fibers of alkali silicatenecessary for the purposes of this invention. This apparatus isdescribed completely in my co-pending application, Serial No. 247,010,filed September 17, 1951, and assigned to the same assignee as thepresent invention, and is referred to herein in order that the inventionmay be readily understood.

As illustrated in FIGURE 1 a hopper may feed small glass balls of about/2 inch diameter to a chamber 12, lined with platinum as at 14 andheated uniform- 1y by coil 16. Coil 16 is positioned over only a lowerportion of the periphery where glass fusion takes place and heatinsulating ceramic material 17 surrounds the remainder of the peripheryfor conservation of heat and maintenance of uni-form temperature. Thebottom wall 18 of this chamber is provided with small openings 20through which glass may exude in the form of strands.

Strands as at 22 emanating from chamber 12 pass over guide roller 24between drawing rolls 26, 28 to guide block 30 having a U-shaped edge32. In horizontal alignment with edge 32 is positioned gas burner 34having a horizontal discharge slot 36 through which a high velocity hightemperature gas blast is discharged to sweep the ends of glass fibers 22extending below edge 32 into chamber 38. A be-lt 40 traveling verticallypast the far end of chamber 38 receives the fibers thereon. The belt 40is driven at a slow speed preferably about 10 feet per minute byapparatus (not shown). A hood 42 to which a vacuum source (not shown) isapplied assists the flow of the fine fibers from the chamber 38 to thebelt.

A suitable composition of the glass of the balls for this fiberformation is about 78.2% silica and 21.8% sodium oxide. 7

Positioned closely adjacent the outer run 44 of the belt is a steelroller 46 driven by a motor and gear box unit 48 at approximately thesame surface speed in feet per minute as the belt 40. The fluffy fibersdeposited in a mat form on the belt at 39 and passing upwardly over thepulley 41 are in their downward course on the outer run 44 wrappedaround the roller 46 to form a tightly plied bat of sodium silicatefibers S0. The thickness of the fluify fibers as they pass upwardly at39 is about of an inch and the thickness of the mass on the roller 46may be preferably about 1% inches for general commercial purposes, thatis the material is plied about 20 times.

It is to be noted that the thin mat at 39 may be ten- 4 sioned slightlyas it is drawn onto the roller 46 the outer plies of the layered bat dueto the increased surface speed at the larger diameter being more tightlywound which is desirable to increase the compactness. If preferred, anautomatic control may be employed to maintain the mat speed constant byvarying the roller rpm. and may be necessary if extremely thick bats areto be produced.

When the plied product has been attained the strand of the fibers movingdown the run 44 is cut at just adjacent the roller, the mass 50 beingpreferably sliced completely therethrough (FIGURE 2) in one operation byknife blade indicated generally at 52.

During the cutting operation the belt 4% may continue to run and thedisconnected fibrous mass will pass downwardly as indicated in dottedlines at 54 and this material may then be wrapped upwardly around theroller 46 from which the first mass 50 has been cut in order to startthe next cycle.

When a series of masses has been attained (FIGURE 3) and flattened outthey are ready for the leaching operation which is performed in a heavywooden box 6i) provided with supports 62 and inlet 64 and an outlet 66.Adjacent the supports 62 there is first placed a layer of acid-resistantsaran es and the first layer of fibers 50 is placed thereon; alternatelylayers of saran and fibers then fill the Wooden box to substantially thetop thereof. The uppermost layer of saran receives thereon a relativelylight Weight wooden cap 7! the weight of this cap 79 is sufiicient toprevent swelling of the fibers of the mass 5% when acid is passed intothe box 60, but does not place a positive pressure on the bats in thesense they are squeezed together thereby; rather the cap Where usedfloats upon the body of glass bats subjected to the leaching agent. Thusin the process of invention the mats 50 stripped from the roller 46 intheir tiered arrangement of the box 60 may be subjected to a continuousflow of an acid solution containing about 5 percent by weight ofsulfuric acid at a temperature of about 180 F.

With the acid penetrating continuously through the box the sodium oxidepresent in the sodium silicate fibers will be leached completely fromthe fibers in about 2 hours. 7

After completion of the acid treatment water may be passed through theinlet 64 to the outlet 66 to free the fibers of excess acid. Thereafterthe light weight cap 70, the saran layers and the fiber layers areremoved from the box 60 and if necessary further washed in water toinsure the complete freedom of the same from acid.

Referring now to FIGURE 4 there is shown an oven 72 in which the bats ofsilica fibers 50 may be stacked between spaced plates 74 supported inthe oven on channels as at 76 for subjection to a temperature of aboutl100 F. to 1200" F. The water vapor is drawn ofi from the productthrough the outlet 78 and the heating is eifected for approximately 3hours in order to insure of complete removal of the combined water.

The product of this heating operation as indicated in FiGURE 5 is thewhite fluflfy coherent mass described hereinbefore.

In connection with the process of invention generally it is to be notedthat it is not necessary to use an acid, but the leaching may beeffected by flowing water at room temperature through the fiberspositioned in the box 60 for a period of about 10 hours.

The percolation of the Water through the box apparently inhibits anytendency of the material to gel.

- Where higher temperatures are used and water is percolated through thematerial the time of leaching may be shortened by raising thetemperature of the water, for example, water at about the boiling pointeffects complete leaching by a third the time required at roomtemperature.

Where water is employed it is preferable to utilize distilled water inorder to avoid the introduction of any impurity into the mass as will beunderstood by one skilled in the art. However in many localities tapwater is entirely suitable, and when the leaching or extraction agentcontains a mineral acid tap waters are generally suitable for theprocess.

High acid concentrations may also be suitably employed, to 20 percent byweight of the mineral acids, i.e., HCl or H 80 being entirely suitable;organic acids may be similarly utilized.

The acids may be at temperatures of up to the boiling point, but someare difficult to handle under this condition requiring special equipmentto prevent corrosion failures and excessive volatilization and thereforelower temperatures are in general preferred, sulfuric acid attemperatures of up to 180 F. being very suitable.

In this latter connection it is to be noted that the acids usedpreferably form a soluble salt with the material leached from the fibersas such may be readily re moved from the silica product by simplywashing the same.

The rate of flow of the leaching acid or water is not critical itgenerally being satisfactory for production purposes to simplycontinuously peroolate the leaching agent. If desired a batch processmay be employed for leaching but in this case it is desirable to changethe leaching agent at frequent intervals in order to avoid any tendencytowards gel formation; thus if water is used at room temperature thewater should be changed every 1-2 hours in the -12. hour treatment forthe alkaline oxide removal.

The monovalent alkalis are preferable for the practice of invention,sodium being preferred, but potassium, lithium and mixtures of thealkalis such as a sodiumpotassium silicate being suitable. The ratio ofsilica to alkaline oxide should be relatively high as the resultantpnoduct having only a small amount of material leached therefrom willhave a consider-able body; a silica to alkaline oxide ratio of about 4:1is entirely suitable for production purposes from the point of view ofbody in the silica fiber.

Repeated experiments have demonstrated that 100% of the alkaline oxidewhich is in the original glass composition is removed in the practice ofthe invention, and accordingly the product of the specific example setout hereinbefore is substantially 100% silica.

The existence of an impurity in the finished product which does notmaterially affect the capabilities of the silica of the fiber may, formany purposes, be tolerated. However 1% of alkaline oxide, as forexample, 1% by weight of Na O in the product lowers the fusion point andelectrical resistance materially.

The presence in the silica of traces of oxides may in many instances betolerated but it is to be clearly understood that the invention involvesan alkali glass, i.e. an alkali silicate system from which the alkalimay be completely removed; the presence of very small amounts of iron,aluminum, calcium, magnesium and other such oxides which may be presentas impurities in the sand utilized for glass forming may in mostinstances be tolerated however, it being important to keep suchquantities loW, as less than 2% total, in order that the fiber producedupon leaching will be self sustaining. Thus where the original glasscontains 78% silica, 21.8% Na O and .2% of other oxides over 78% of theoriginal fibers remain after leaching and accordingly the body of fibersis self-supporting. This latter factor is considered to be importantWith respect to the ability of the fibers to withstand, in compacted batform, Without exterior support, the handling and other processesinvolved in the inventive method.

With regard to production arrangements it is to be noted that the alkalisilicate fiber should be leached within a reasonable time afterformation thereof or the fiber stored under such conditons thatself-deterioration will not occur. Thus the fibers should not be leftfor an undue length of time in a humid atmosphere. A time of storage ofless than two days under normal Weather conditions is generallysatisfactory although the process is preferably practiced as acontinuous one.

The product of the invention is a strong material suitable for use athigh temperatures as in the tail pipes of jet aircraft; the product alsohas particular value in fire-entry suits and may of course be used inall places where fibrous glass is normally utilized and will providesuperior strength in those environments.

It will be understood that this invention is susceptible to modificationin order to adopt it to different usages and conditions and accordingly,it is desired to comprehend such modifications within this invention asmay fall within the scope of the appended claims.

I claim:

1. A process for producing a fibrous hat of substantially pure silica,comprising forming a compacted hat of siliceous fibers consistingessentially of silica and an alkali metal oxide, the ratio of silica tosaid alkali metal oxide being in the order of about 4:1 and said fibershaving a diameter less than 2 /2 microns, and flowing an aqueousleaching solution through said hat of fibers until substantially all ofthe alkali is extracted therefrom.

2. A process as defined in claim 1, wherein the leaching solutioncontains an acid which Will form a water soluble salt with the alkali,and after substantially all of the alkali has been extracted from thefibers flowing water through the fibers to wash the salt from thefibers.

References Cited in the file of this patent UNITED STATES PATENTS2,165,280 Lannan July 11, 1939 2,461,841 Nordberg Feb. 15, 19492,494,259 Nordberg Jan. 10, 1950 2,692,220 Labino Oct. 19, 1954

1. A PROCESS FOR PRODUCING A FIBROUS BAT OF SUBSTANTIALLY PURE SILICA,COMPRISNG FORMING A COMPACTED BAT OF SILICEOUS FIBERS CONSISTINGESSENTIALLY OF SILICA AND AN ALKALI METAL OXIDE, THE RATIO OF SILICA TOSAID ALKALI METAL OXIDE BEING IN THE ORDER OF ABOUT 4:1 AND SAID FIBERSHAVING A DIAMETER LESS THAN 2 1/2 MICRONS, AND FLOWING AN AQUEOUSLEACHING SOLUTION THROUGH SAID BAT OF FIBERS UNTIL SUBSTANTIALLY ALL OFTHE ALKALI IS EXTRACTED THEREFROM.